Three different TiO2-SiO2 gels (Xerogel, Carbogel andAerogel) are more active acid catalysts than other reference samples usedhere. As deduced from FTIR, XRD and XANES studies, the structural propertiesof these gels are quite different to each other, thus revealing the stronginfluence of the drying treatment. It is found that the degree of Si-O-Tilinking and the surface acidity follows the same trend (X 〉 C 〉 A). Weconclude that supercritical drying at 600 K and 190 bars can induce Tileaching followed by redeposition in the narrower pores of the gel. Theseeffects modify both the textural and surface chemical properties of theresulting material.

Anomalous revolving stacking crystal growth of β-type vanadium oxide hydrateformed by hydrothermal treatment was studied by transmission electronmicroscopy.

Formation of V4+ upon UV-irradiation in the V2O5 · n H2O wasconfirmed and the layered structure of this material was discussed on thebasis of an ESR analysis of the species produced therefrom in combinationwith spectral change upon H2O adsorption.

ZrO2 coatings were obtained by the the alkoxide route anddeposited onto stainless steel using the dip coating technique. The startingsolutions were prepared by mixing zirconium tetrabutoxide, isopropanol,acetylacetone. The water content for the hydrolitic reaction arose from theatmosphere moisture.

Useful information for the structural organization of the zirconia/steelinterphase is given by XPS analysis.

It is found that during firing treatment, the main components (Fe, Cr, Ni)of the stainless steel diffuse into the ceramic coating. XPS data allow todescribe the chemical composition variation from the bulk substrate to theouter coating surface.

Thermal stability of a novel rubbery ORMOSIL of condensed tetraethoxysilane(TEOS) and polydimethylsiloxane (PDMS) was investigated along with methodsby which to improve this stability. Based upon literature review of siloxanesystems, modifications of the base ORMOSIL system was made which includedsubstitution of polydimethyldiphenylsiloxane (PDMDPS) for PDMS, addingantioxidant, and adding iron compounds. Relative enhancement wasinvestigated in terms of resilience measurements, and was also analyzed withthermo-gravimetric analysis (TGA) and differential thermal anaysis(DTA).

The carbon retention patterns based on evolution of FT-IR spectra atdifferent calcination temperatures for ZrO2 gels derived fromZr-n-propoxide-acetylacetone-water-isopropanol system are examined indetail. For most captured carbon species, carbon can be depleted atrelatively low temperature of about 400°C. However, for lattice-includedspecies, especially those incorporated into lattice during phase transition,a temperature around 900°C is needed to eliminate carbon in the gels. It isfound that water treatment alone does not provide new routes for carbonretention in as-prepared ZrO2 gels. When gels are pre-treatedwith Ni2+ and water, new forms of carbon containing species canbe observed. This is attributed to an inter-diffusion of Ni2+ and ZrO2 matrix and the catalytic effect of resultant solidsolution NiO-ZrO2 on the retained carbon.

The crystallization behaviors of stoichiometric feldspar gels and glassesbefore and after seeding have been compared, and the role of epitaxy intheir crystallization upon seeding has been studied. The crystallizationproducts were mainly determined by X-ray diffraction (XRD) analysis andepitaxy upon seeding was examined with a scanning electron microscope (SEM),and energy dispersive spectrometry (EDS). It was found that uponisostructural seeding, Na-and K-feldspars crystallized epitaxially fromtheir gels and/or glasses. Little or no seeding effect was found in CaAl2Si2O8 and SrAl2Si2O8 gels and glasses.Isostructural seeding in BaAl2Si2O8 gelsincreased the formation of Ba-feldspar (monoclinic celsian) epitaxially,whereas without seeding hexacelsian was the crystallization product.

The infrared vibrational modes of sol-gel derived optical silica monolithsdepend upon thermal treatments and chemical environments, as shown byFourier transform infrared spectroscopy (FTIR). A semi-empirical quantummechanical theory (PM-3 in MOPAC 6.1) is used to analyze the structuralchanges responsible for the spectral shifts. Optimized structures of2-member, 3-, 4-, 5- and 6-member rings of SiO2 are calculated.The force constants for the molecular bonds in the rings are obtained andconverted to the associated vibrational spectra for the rings. The peakposition of the asymmetric transverse optical (AS1TO) mode of therings shifts from 1070 cm−1 for 2-member rings to 1100 cm−1 for 3-member rings, 1150 cnr1 for 4-memberrings, 1140 cm−1 for 5-member and 1120 cm−1 for6-member rings. The IR data show a 38 cm”1 shift of the AS1TO mode as the gel-silica density changes from 1.1 g/cc to2.2 g/cc. Thus, the intensification and shift of the AS1TO modein the gel-silica to higher wave-numbers corresponds to a change in thedistribution to larger silicate size rings.

The grain boundary phase of silicon nitride containing additives Y2O3 and Nd2O3 has beenstudied by means of a newly developed 300kV field emission ATEM. Thecomposition of the two-grain boundary phase of about 1 nm thick issuccessfully determined. It is then found that the compositions among thegrain boundaries are not the same and the additives of Y2O3-Nd2O3 are poor in thetwo-grain boundary, while they are rich in the triple points.

Compositions from the systems Pb-Mn-B-O and Pb-Mn-Te-0 are used tosynthesize glass-ceramics obtained by solid state reactions and fromsupercooled melts. By casting on a metal plate or by quenching with the aidof twin rollers the melts are cooling. The glass-crystalline materials areobtained after heating glasses from the combination of PbO-MnO-B203 and PbO-MnO-TeO2 with theaddition of La203 from 10 to 50 wt.% and the formationof the crystalline phases is determined.

Broadband fluorescence and fluorescence line narrowing (FLN) spectra arepresented for Eu3+ ions in Eu2O3-SiO3 and Eu2O3-Al2O3-SiO3systems prepared by the sol-gel process. Clustering of rare earth ions insilica glass can be a limiting factor in the design and engineering ofoptical device materials. The addition of Al2O3 isknown to help disperse rare earth ions in sol-gel silica. In order todevelop a more detailed understanding of how Eu3+ is incorporatedin these materials, time-resolved, laser-induced FLN studies at 77 K havebeen performed using a pulsed dye laser to selectively excite subsets ofions in the inhomogeneously broadened 7F0⇆ 5D0 manifold. Fluorescence spectra are discussed interms of rare earth ion clustering, energy transfer, and bonding sitesymmetry. It is concluded that Eu3+ ions cluster in sol-gelsilica and that the addition of alumina assists in dispersing Eu3+ ions.

The morphology of titanium dioxide aerogel was studied using a variety ofcomplementary techniques that include: nitrogen adsorption, Small-AngleNeutron Scattering (SANS), scanning and transmission electron microscopies(SEM/TEM) and X-ray diffraction. Since these techniques sense differentcomponents of the microstructure, global parametrization should coalesce theresults into a uniform framework.

Lattice parameters of some different chromium-doped mullites obtained by asol-gel route and sintered at 1650° C have been determined from X-RayDiffraction data as a function of both temperature and Cr contents. Profilerefinements on the X-ray diffraction diagrams have been carried out, showingthat, at temperatures between 800° and 1535° C, an anisotropic thermalexpansion takes place for the a and blattice parameters of the Cr-doped mullite. We show that this anisotropicexpansion is dependent on the temperature increase and the chromium contentfor the different compositions of the mullite crystals.

Poly(l,4-phenylene)-bridged and poly(1,6-hexylene)-bridged silsesquioxanes(PPS and HPS) were prepared by the sol-gel process. The surface areas andpore diameters of these porous xerogels were obtained by BET and BJHmethods, respectively. These porous materials were used as a confinementmatrix for the growth of small-sized semiconductor and transition metalclusters. Quantum-sized CdS particles in PPS (approximately 58+12 Â) and HPS(91+16 Â) matrices were prepared by first soaking the xerogel in a CdCl2 solution. Following a washing with water, a Na2Ssolution was then added. EDAX and electron diffraction techniques were usedto identify the CdS particles. The particle sizes of CdS in PPS and HPS weredetermined by both UV measurements and from TEM images. Small-sized Crclusters were prepared in dried xerogels by an internal doping method. MixedCr/CdS phases were also prepared by internal loading of a chromium metalprecursor. Following deposition of CdS the xerogel was heated at 120 °Cunder high vacuum, resulting in formation of intimately mixed phases of Crmetal and CdS. Changes in morphology, in particular the surface area andpore size distribution were noted. A decrease in surface area and anincrease in pore size were observed as a result of Cr metal deposition.

Quantum-size silicon enriched regions were formed in silica porous glassesobtained by three different technologies. Processing in the spark dischargeand carbon reduction of silicon dioxide in the solid phase were performedfor this purpose. All fabricated specimens have been investigated inrelation to their electrical and photoluminescence (PL) properties. Apronounced increase of visible luminescence and single-type changes in thea.c. conductivity were registered in all cases.

Pd colloid containing Ormocers (organically modified ceramics) havebeen prepared from Pd amino complexes of the type Pd[NH2CH2CH2NH(CH2)3Si(OMe)3]2ac2by hydrolysis and condensation (sol-gel reaction) of the silane togetherwith Si(OEt)4 and Si(OEt)3(CH2)3OCH2CHCH2O.The amino complex formation is necessary to avoid spontaneous reduction anduncontrolled colloid formations in the liquid phase. This synthesis routeleads to Pd colloid containing powders and coatings on glass. By thermalcuring (temperatures up to 500 °C) using different atmospheric conditions (N2, Ar, H2/N2) brown to deep blackcoatings on glass with transmission values from 80 to 0 % can be obtained.The average particle size can be controlled by varying the molar ratio ofthe used Pd salt (Pd(ac)2) and the aminosilane.

Dynamic oscillatory experiments are used to monitor the gelation of theborosilicate systems prepared through the sol-gel process from metalalkoxides. The rheological experiments show that tan δ = G”/G’ isindependent of frequency at the gel point in agreement with the results ofothers on organic gelling systems. The dynamic moduli at the gel pointfollowed power-law behavior with respect to frequency. The power-lawexponent is found to be ∼0.70. The apparent fractal dimension, dp, of thenetwork cluster at the gel point is determined. The dF values forthe samples ranged from 2.5 to 3.8 depending on the final structure of theevolved products at the gel point. The large values (dF > 3)exclude a simple geometric interpretation of the results. The effect ofprocessing parameters, such as composition of reactants and temperature, onthe resulting microstructures near the gel point is discussed.

Spherical particles of lead titanate, PbTiO3, (PT) were preparedfrom partially hydrolyzed alkoxide solutions modified with benzoic acid.Modified and aged alkoxide solutions were added dropwise to isopropylalcohol, forming particles (0.2 to 1.0 μm in diameter). FTIR spectroscopyresults demonstrate chelation of the PT alkoxide which prevented theformation of an extended gel network. Diffuse reflectance FTIR (DRIFT)spectra indicate the benzoate ligands are present until 450°C; TGA resultsshow significant weight loss at 450°C. PT particles crystallize into theperovskite phase at =450°C, as determined by DTA and XRD. The relatively lowcrystallization temperature may be due to the effect of benzoate ligands onamorphous structure and presence of internal surfaces.

Low-hydroxyl organically modified silicates (ORMOSILS) were fabricated by anon-hydrolytic reaction between methyl-modified silicon halides and tertiarybutyl alcohol under controlled atmosphere. The gels were characterized byDTA and TGA., FTIR, 1H NMR and 29Si NMR. The solutionswere doped with anhydrous Erl3, which was dissolved in the solprior to gelation. Er3+luminescence in the gels was observed at570 nm under excitation at 488 nm.

Factors controlling hydrothermal synthetic procedures are not wellunderstood. A good knowledge of the solution chemistry of precursor speciesis the best reference for the design of rational procedures. Examples of thepredictive character of simple models in order to rationalize complexsyntheses are discussed in detail.